Protein synthesis, ATP unnecessary for ..

Lipoprotein lipase is the major enzyme responsible for synthesis ..

This flowchart shows that the energy used by the body for its many activities ultimately comes from the chemical energy in our food. The chemical energy in our food is converted to reducing agents (NADH and FADH2). These reducing agents are then used to make ATP. ATP stores chemical energy, so that it is available to the body in a readily accessible form.

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3b3 forming a hexagonal ringed structure with a central cavity,)γ subunit which spans the center of the 3b3 ring. Energy transduction (necessary to capture the negative free energy change associated with the collapse of the proton gradient to drive the positive free energy change for ATP synthesis) occurs between the two subunits. Noji investigated the structural changes in the γ subunit, wishing to get direct experimental evidence for Boyer's three-state conformational model (L-O-T) for ATP synthesis.

Hence the overall reaction for the oxidation of NADH paired with the reduction of O2 has a negative change in free energy (G =); i.e., it is spontaneous. Thus, the higher the electrical potential of a reduction half reaction, the greater the tendency for the species to accept an electron.

Glossary | Linus Pauling Institute | Oregon State University

ATP is also used to drive peptide bond (amide) synthesis during protein synthesis. From an energetic point of view, anhydride cleavage can provide the energy for amide bond formation. Peptide bond synthesis is cells is accompanied by cleavage of both phosphoanhydride bonds in ATP in a complicated set of reactions that is catalyzed by ribosomes in the cells. (This topic is considered in depth in molecular biology courses). The figure below is a grossly simplified mechanism of how peptide bond formation can be coupled to ATP cleavage.

Protein Synthesis -Translation and Regulation

ATP is the most important "free-energy-currency"molecule in living organisms (see Figure 2, below). Adenosinetriphosphate (ATP) is a useful free-energy currency because thedephosphorylation reaction is very spontaneous; i.e., itreleases a large amount of free energy (30.5 kJ/mol). Thus,the dephosphorylation reaction of ATP to ADP and inorganicphosphate (Equation 3) is often coupled with nonspontaneousreactions (e.g.,Equation 2) to drive them forward. The body's use of ATPas a free-energy currency is a very effective strategy to causevital nonspontaneous reactions to occur.

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As these coupled reactions (e.g., Equations 2-4)occur, we use up ATP. In a typical cell, an ATP molecule is usedwithin a minute of its formation. During strenuousexercise, the rate of utilization of ATP is even higher. Hence,the supply of ATP must be regenerated. We consume food to provideenergy for the body, but the majority of the energy in food isnot in the form of ATP. The body utilizes energy from othernutrients in the diet to produce ATP through oxidation-reductionreactions (Figure 3).

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The first process in the breakdown of glucose is glycolysis (Equation 5), in which glucose is broken down into two three-carbon molecules known as pyruvate. The pyruvate is then converted to acetyl CoA (acetyl coenzyme A) and carbon dioxide in an intermediate step (Equation 6). In the second process, known as the citric-acid cycle (Equation 7), the three-carbon molecules are further broken down into carbon dioxide. The energy released by the breakdown of glucose () can be used to phosphorylate (add a phosphate group to) ADP, forming ATP (). The net reactions for glycolysis (Equation 5) and the citric-acid cycle (Equation 7) are shown below. (Note: In the equations below, glucose and the carbon compounds into which glucose is broken are shown in red; energy-currency molecules are shown in green, and reducing agents used in the synthesis of ATP are shown in blue.)

Table 2 lists the reduction potentials for each of thecytochrome proteins (i.e., the last three steps in theelectron-transport chain before the electrons are accepted by O2)involved in the electron-transport chain. Note that each electrontransfer is to a cytochrome with a higher reduction potentialthan the previous cytochrome. As described in the box above andseen in Equations 14-19, an increase in potential leads to adecrease in G (Equation 13), and thusthe transfer of electrons through the chain is spontaneous.

It should now be clear why the enzymes for oxidative phosphorylation in aerobic conditions are membrane bound. Only in this way could a proton gradient be established. Protons must be vectorially transferred in one direction only for a gradient to be established!

An oxidation-reduction reaction consists of an oxidation half reaction and a reduction half reaction. Every half reaction has an electrical potential (By convention, all half reactions are written as reductions, and the electrical potential for an oxidation half-reaction is equal in magnitude, but opposite in sign, to the electrical potential for the corresponding reduction (i.e., the opposite reaction). The electrical potential for an oxidation-reduction reaction is calculated by

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Recent experiments (Wantanbe, 2010) using immobilized ATPase and magnetic tweezers have addressed the timing of substrate binding and product release when the enzyme is run in reverse (ATP hydrolysis). On rotation of the gamma subunit, the three binding sites change properties. In hydrolysis, ATP binds to the open site, and helps promote the 120 degree rotation. In the next step, ATP is hydrolyzed. In final step, products dissociate. Pi dissociation occurs last from the third site. Hence each of the 3 beta binding sites have different roles. One binds substrate, one performs catalysis, and third releases products. Assuming the synthesis pathway is the reverse of the ATPase reaction, the final release of Pi in ATP cleavage predicts that Pi binds first in the synthetic direction. This would preclude the binding of ATP next which is critical since its concentration during synthesis can be 10x higher than that of ADP. As Pi is bound first, only ADP, not ATP can bind next.

which is also known as complex V, is responsible for ..

Table 2 shows that the electrons are transferred through theelectron-transport chain because of the difference in thereduction potential of the electron carriers. As explained in thegreen box below, the higher the electrical potential (of a reduction half reaction is, the greater the tendency is forthe species to accept an electron. Hence, in theelectron-transport chain, electrons are transferred spontaneouslyfrom carriers whose reduction results in a small electricalpotential change to carriers whose reduction results in anincreasingly larger electrical potential change.